The present invention relates to the control of warp threads on weaving machines and in particular, although not exclusively, to the control of warp threads on Jacquard machines, e.g. selvedge machines.
In a known selvedge machine, each warp thread from a shed is threaded through a heald eye secured to a heald wire. The lower end of the wire is attached to one end of a spring which biases the lower end of the cord downwardly. The upper region of the wire passes around a floating pulley, and its end is secured to a fixed mounting. The pulley is connected to, and suspended from, a further floating pulley around which a loop passes. Each end of the loop is connected to a different hook, and the upper region of each hook co-operates with a different griffe bar. In use, the griffe bars alternately reciprocate up and down and, when the warp thread is required to remain in the upper position, the ends of the hooks move up and down with the griffe bars. With such a movement, the pulleys remain in the upper position.
When it is required to lower the warp thread, a needle, co-operating with the hooks, is caused to move, when one of the griffe bars is in the lower position, to push the hook off that griffe bar so that the hook remains in the lower position when the associated griffe bar rises. When this occurs, the pulleys are allowed to fall when the other griffe bar and hook move downwardly, and the spring pulls the wire downwardly to move the warp thread to the lower position. The movement of the needle is controlled by a movable operating card, having appropriate openings.
The griffe bars and hooks are expensive to manufacture and complicated to operate satisfactorily over long periods, as the griffe bars reciprocate in a straight direction, this causing considerable stress on those bars, and the hooks are required to move in two directions, one being vertical as the griffe bars reciprocate and the other being horizontal as the hooks are pushed off the griffe bars. Furthermore, the griffe bars and hooks tend to become worn fairly rapidly as a result of their operating action. An additional disadvantage is the mechanical operation of the needle and card which present further mechanical components liable to wear and break down. As a result of the complexity of operation of the prior machine, only a relatively low operating rate of around 400 revs or cycles per minute is able to be achieved.